The present invention relates to propeller systems and more particularly to counter rotating, open rotor propeller systems.
Most gas turbine engines on commercial airliners are known as turbofans. They typically have a fixed pitch fan on the front of the engine with a shroud around it. Some gas turbine engines feature an open rotor propeller system that includes a pair of rotors supporting the propeller blades. The rotors and blades may be mounted behind the gas turbine engine that is supplying power to the rotor system. These propeller blades are not shrouded. This configuration is commonly referred to as a “pusher” configuration.
One variation of the pusher configuration has the hot exhaust gas emanating from the gas turbine engine directly in front of the root of the propeller blades. This hot gas path may attain temperatures of approximately 900° F. (482° C.). The hot gas does not mix with the ambient air stream flowing over the system at this important point of the engine, but, rather, dissipates in the exhaust area behind the aircraft. Depending on the material used to construct the propeller blades, thermal protection may be required to prevent damage to the structural portion of these blades. Loss of the material properties is also of concern.
Open rotor propeller systems include a spinner, which is the aerodynamic body of revolution in the center of the propeller. The spinner is commonly used to provide a smooth aerodynamic contour that covers the hubs and actuators incorporated in the propeller. In this configuration, the spinner surface is exposed to the high temperature exhaust gas from the gas turbine. Inside the spinner is the hub's structural part for holding the blades in place and keeping them from being thrown out by centrifugal force. Also inside the spinner is the pitch change mechanism that allows the pitch of the blades to change, depending upon the thrust demands from the gas turbine engine.
The blades themselves are not protected by the shroud in conventional designs. The blades, typically formed from epoxy and fiberglass, or other composites, are at risk in the 900° F. (482° C.) exhaust gasses.
Spinners are at this time made from materials that protect the inside of the spinner where the pitch change mechanism is, whether it is electric or hydraulic or another mechanism. The materials are thermal insulators, often multi-layer composites that have high thermal insulation. The spinner shroud is not doing any structural work and only has to be strong enough to hold itself together.